PROJECT SUMMARY/ ABSTRACT Prior research indicates that a systemic lack of well-being in our nation is majorly contributing to growing populations of individuals with poor mental health. On the other hand, studies show that flourishing adults with high-levels of psychological well-being (PWB) ? the core elements of human development that lead person to achieve self-fulfillment in life ? have the lowest prevalence ratesof mental disorder or comorbidity. Although various PWB interventions, such as contemplative and positive practices have been shown to effectively promote PWB in targeted groups, to date, most studies of these interventions have lacked the ability to rigorously test their real-world efficacy in terms of how success varies from person to person and amidst daily life challenges. As a solution, we propose employing the ecological momentary assessment (EMA) design to create an integrated tool for (1) rigorous, multifaceted assessment of PWB and (2) delivering PWB interventions in real life settings, with person-centered statistical inference tailored for developing and evaluating EMA-based approaches to increase PWB. EMA is a potential intervention delivery platform that could enhance the efficacy and implementation of PWB interventions. EMA is a technology-based research approach aimed at capturing the ongoing stream of individuals' behavior in real-world settings, to maximize the extent to which research findings generalize to everyday life. EMA's accessible delivery methods use wearable or smartphone technologies that most people own or could easily obtain. By design, EMA impacts engagement ? a key element of PWB ? and intervention adherence. EMA also offers benefits associated with intensive monitoring to promote adherence and insight into daily variability which can predict outcomes. Multiple prior studies have used the EMA design for PWB- EMA, which we define as any EMA design applied to assess elements of PWB, however these studies have yet to systematically examine the pathways through which PWB-EMA can affect PWB. Furthermore, research has yet to systematically test the efficacy of PWB-EMA as a platform for PWB intervention delivery and assessment ? which we term PWB-EMAI (PWB-EMA-intervention). The proposed research involves two arms: firstly, to study the unique role of PWB-EMA in facilitating PWB in everyday life settings; and secondly, to build up a methodological toolkit to test PWB-EMAI with contemplative and positive intervention elements in everyday life settings. Based on mounting empirical evidence, psychology researchers are calling for new investment in U.S. mental health research and services to rigorously implement interventions that promote PWB and foster mental health in our population. Our proposal answers this call by offering innovative methodological assessment that elucidates individual differences in how PWB-EMA (1) is a unique facilitator of PWB, (2) can be used to efficiently deliver a PWB intervention, and (3) within-person dynamics in PWB elements, and how these relate to intervention success. The proposed study will use existing data from a parent study that conducted a PWB- EMA and PWB-EMAI using randomized control design. We will measure the success of each intervention with advanced longitudinal analyses with unique advantages for rigorous, real-time assessment. Upon completion this study aims to disseminate methodological tools for future researchers and to advance knowledge about how PWB-EMA can be used to assess and improve PWB interventions, in order to deliver lasting benefits to researchers, public health, and society as a whole.